As demand on the world's communication networks increases, new protocols emerge. One such protocol is called Generalized Multi-Protocol Label Switching (GMPLS). GMPLS enhances the MPLS architecture by separating the control and data planes of various networking layers. GMPLS enables a seamless interconnection and convergence of new and legacy networks by allowing end-to-end provisioning, control, and traffic engineering.
A label-switched path (LSP) may be subject to local (span), segment, and/or end-to-end recovery. Local span protection refers to the protection of the link (and hence all the LSPs marked as required for span protection and routed over the link) between two neighboring network nodes. Segment protection refers to the recovery of an LSP segment between two nodes (i.e., the boundary nodes of the segment). End-to-end protection refers to the protection of an entire LSP from the ingress (source) node to the egress (destination) node.
There are three fundamental models for span protection. The first model is referred to as 1+1 protection model, the second model is referred to as a 1+N protection model, and the third model is referred to as shared (mesh) protection model. With the 1+1 protection model, a dedicated, protection path is pre-assigned to protect a working path. LSP traffic is permanently bridged onto both paths (working and protection) at the ingress node, and the egress node selects the signal (i.e., normal traffic) from the working or protection path. Under unidirectional 1+1 span protection, the ingress node and the egress node act autonomously to select the signal from the working path or the protection path. Under bi-directional 1+1 span protection, the ingress node and the egress node coordinate the selection function such that they select the signal from the same path: working path or protection path.
With the 1+N protection model, a protection path is pre-assigned to protect a set of N working paths. A failure in any of the N working paths results in traffic being switched to the protection path. This is typically a two-step process: first the data plane failure is detected at the egress node and reported to the ingress node, and the LSPs on the failed path are moved to the protection path.
With the shared (mesh) protection model, a set of N working paths are protected by a set of M protection paths, usually with M≦N. A failure in any of the N working paths results in traffic being switched to one of the M protection paths. This is typically a three-step process: first the data plane failure is detected at the egress node and reported to the ingress node, a protection path is selected, and the LSPs on the failed path are moved to the protection path.